This invention relates to a multiuser bit-mapped graphics system.
An architecture commonly used for color raster scan graphics display systems is a frame buffer with a color map. A terminal or work station will have a number of overlaying bit planes associated with it. A bit plane is conceptually a planar arrangement of memory cells with addressability equal to or greater than that of the display surface. Looking down through these planes provides a data word associated with a pixel (picture element). The assignment of these pixel data to actual display surface locations is often fixed, but some display systems allow some control here for improved dynamics. The pixel data word is usually translated by a color look-up table (CLT) to obtain the display appearance currently assigned to that particular data value.
In order to provide features such as fast window management, fast magnify, smooth roam, flexible bit-plane expansion and others, some systems are built with an increased complexity such as random access over the pixel data bus between the color look-up table and the bit planes. The required speed might be supported by a special wide pixel data bus transferring multiple pixels at a time. The use of random access and the required fast data rates of such systems limits the size of such a system to a single display or possibly a small number of displays at reduced addressability.
The straightforward approach to a multi-user graphic system is to have a plurality of display systems, one for each user. The display systems might be external or internal to the graphics host responsible for supplying image data for the bit planes, however, the systems each operate distinctly. Each system is assigned to a single user and has one identifiable set of hardware associated with it, the bit planes for each user being a part of that hardware. One disadvantage of this system is that each user must always have the maximum amount of hardware required for any application that would be run by that user.